A 1.5 tonne building block has already been produced for demonstration purposes

The European Space Agency (ESA) is looking to build a lunar base with 3D printing using local materials on the moon.

The idea behind this project is to offer settlement for astronauts on the moon while using less of Earth's resources to do so.

ESA has partnered with architectural firms like Foster + Partners to see whether lunar soil could be used for a 3D printed lunar base. In fact, Foster + Partners has already designed a "catenary" dome, which is a hollow closed-cell structure complete with a wall that protects against space radiation and micrometeoroids.

A 1.5 tonne building block has already been produced for demonstration purposes, as seen below:

The 3D structures are built layer-by-layer. The lunar material would be combined with magnesium oxide, which turns it into a "paper" to be printed with. Then, for the "ink," a binding salt is added to transform the material into a solid. The architects are trying to create a structure that can handle the harsh weather and environment that the moon can have.

“3D printing offers a potential means of facilitating lunar settlement with reduced logistics from Earth,” said Scott Hovland of ESA’s human spaceflight team.
“The new possibilities this work opens up can then be considered by international space agencies as part of the current development of a common exploration strategy.”

Good idea. The moon has a high iron content. Use a nuke reactor to power a smelting process. We can build the heavy machinery from scratch on site. This bubble dome thing would be good for the initial landing site and living quarters until we could get to the point we could build a tunneling machine.

Because really you must be underground. Just a handful of micrometeorites would massacre everyone inside this thing without atmosphere to slow them down. Radiation is another concern that you need a bunch of hard rock to defeat. It's the perfect solution for a long-term habitation.

Plus the real upswing to having a lunar base is that you can use it to launch craft to other places with much less gravity to overcome than on Earth. We could build a bigass railgun and strap an entire rocket on top of it. Use the railgun to launch and then the rocket can use it's fuel to get back home.